Typically, multiplexer assemblies that are used in aerospace applications are designed to have insignificant dimensional changes as a result of changes in temperature so that the spacing between filters does not appreciably change with changes in temperature. As a result, aerospace waveguide assemblies are typically manufactured from low expansion materials (i.e. materials that have low coefficients of thermal expansion (CTE)) such as INVAR™ or titanium. However, it is often necessary to physically attach waveguides to a panel on the body of a spacecraft which is generally manufactured from lightweight materials with relatively high coefficients of thermal expansion (CTE), such as aluminum. Accordingly, when low CTE waveguide assemblies are coupled to high CTE spacecraft bodies, substantial physical strain between the structures results with a corresponding increase in faulty mechanical operation.
Accordingly, it is desirable to provide a waveguide assembly for space application that will experience changes in dimension (i.e. length) that correspond with the dimensional changes of the spacecraft panel. Temperature compensating waveguide assemblies use a variety of mechanical deformation techniques to compensate for temperature-dependent volume changes in a waveguide that cause shifts in the frequency profile of a waveguide. Prior art approaches utilize various mechanical arrangements of materials having different coefficients of thermal expansion to cause deformation of waveguide walls in response to changes in temperature. However, these assemblies suffer from practical disadvantages that detrimentally affect their suitability for space application.
For example, U.S. Pat. No. 5,428,323 to Geissler et al. discloses a waveguide assembly that includes a waveguide having walls defining a cavity. A frame surrounds the walls of the waveguide having a coefficient of thermal expansion less than that of the waveguide. First and second connecting spacers are attached in between the frame and the waveguide and serve to transmit heat expansion related forces to the waveguide walls that causes deformation of the waveguide walls. While the sectional frame allows expansion along its length, the structure requires an external frame and accordingly the overall assembly is cumbersome and is not well suited for space application.
U.S. Pat. No. 6,002,310 to Kich et al. discloses a resonator cavity end wall assembly which comprises a waveguide body and two end wall assemblies, where each end wall assembly includes a bowed aluminum plate and an INVAR™ disk, attached to one another at the periphery thereof. The INVAR™ disk includes a relatively thick outer annular portion and a relatively thin inner circular portion. The bowed aluminum plate bows in response to increased temperature, thereby counteracting the expansion of the waveguide body. When temperature increases, ‘oil can’ bowing of the aluminum plate within the end wall assemblies causes the cavity diameter to increase and the axial length to be reduced. Accordingly, this assembly is not suitable for aerospace application where in the case of increased temperature, the axial length of a waveguide should match an increase in axial length of a spacecraft panel.